When measuring relative humidity with the aid of sensor devices having capacitive humidity sensor elements, measuring errors often occur in the high-humidity range (rH>95%). In particular, relative humidity readings that are too high are sometimes measured in this connection. A number of causes may be responsible for this effect, for example, the general saturation behavior of the humidity-sensor elements, the beginning condensation and the resulting short-circuits at the contacts of the humidity-sensor elements, etc.
European Published Patent Application 0 801 302 describes a method and a device for determining the absolute humidity, where the device is operated in a heating mode at or above a particular humidity limit value. In heating mode, the temperature of the utilized capacitive humidity-sensor element is adjusted to a constant humidity-sensor capacitance. This occurs in this measuring range, i.e., in the high humidity range, by suitably heating the humidity-sensor element with the aid of a temperature-sensor element, which is situated adjacent to the humidity-sensor element in the sensor device. In the high-humidity range, the specific, absolute humidity may then be ascertained from the measured heating current and the known capacitance of the humidity-sensor element. If necessary, in order to still be able to ascertain specific, relative humidity rH in addition to the absolute humidity, where the relative humidity represents the desired quantity to be measured in many different applications, knowledge of ambient temperature Ta is also required. This means that a further component in the form of a temperature sensor is necessary for measuring ambient temperature Ta. This may result in an increased total expenditure within a conventional device, when, in addition to or in place of the absolute humidity, relative humidity rH is also needed as a measured quantity.